Groton - The local firefighters who rushed to the Portsmouth Naval Shipyard last week say the USS Miami blaze was the most intense, challenging fire they've ever encountered.

"There was stuff burning that I didn't even know could burn on a submarine," John Dwire Jr., one of the firefighters, said Tuesday.

Deep inside the hull, Dwire said, he had to cut through the burning wires and cables overhead and then duck or crawl just to get to the fire in the forward section of the Groton-based attack submarine.

The Miami (SSN 755), which was at the shipyard for maintenance and upgrades, caught fire May 23 and burned until early the next day, damaging the torpedo room, command and control spaces and berthing areas. The reactor had been shut down for more than two months at the time and the nuclear propulsion spaces were not affected, according to the Navy. No weapons were on board.

The cause of the fire has not been determined. U.S. Sen. Richard Blumenthal said Tuesday he has heard the repairs could cost as much as $1 billion.

The Submarine Base Fire Department sent 12 firefighters who are trained to fight fires on submarines to the shipyard. Many of the other firefighters who responded from New Hampshire, Maine and Massachusetts had never been on board a submarine before.

The Groton firefighters jumped into three SUVs and drove 170 miles to the shipyard. Peter Woodbury, a captain in the department, said the incident commander "was quite happy to see us."

Down a hatch, they made their way into the dense smoke and intense heat. They waded through a foot of water on the decks from the hoses and used bolt cutters and battery-powered saws to clear the debris and construction staging that was inside the submarine for the maintenance work.

They fought the fire in tight spaces filled with steam until the air supply they carried in tanks ran low and they had to leave.

"If we run into a problem in a structure fire, we can take out a window or breach a wall to get to a safer location," Woodbury said. "We can't do that in a sub."

"Everything turned to steam," Dwire said. "It got really hot fast, and you couldn't see in front of you. I saw the glow from the fire here and there and directed the hose to the glow."

Dwire said he made his way out, took a breath, filled his tank and "got back into it."

"That's what everybody was doing," he said.

Jeffrey Post, a captain in the department, went inside the submarine five times. Most of the others went in two or three times.

Post was in the torpedo room when he stepped forward to a spot where the metal plates for the floor had been removed. A sailor grabbed him and pulled him back. Some of the other firemen got tangled in wires. Seven firefighters from other departments received minor injuries.

Arthur Keaten, a Groton firefighter, said while the fire "takes top billing for being the most challenging," he never doubted the crews would extinguish it.

"I thought we may have to pull out and regroup, but we are going to get this," he said. "It was an awesome accomplishment."

"Firefighters don't go home until the fire is out, whether it takes an hour or 25 hours," said Assistant Fire Chief Robert Kelley.

The leadership of the submarine base plans to recognize the Groton firefighters for their efforts Thursday.

EB stands ready

The cause of the fire has not been determined because the damage assessment and investigation are ongoing, Deborah White, a spokeswoman for the Portsmouth Naval Shipyard, said Tuesday.

A Los Angeles-class submarine built by Electric Boat at a cost of $900 million, the Miami was commissioned at the Naval Submarine Base in Groton in 1990. It arrived at the shipyard in March for a 20-month overhaul.

Blumenthal, D-Conn., said the initial estimates put the cost of repairing the submarine at anywhere from $700 million to $1 billion, and he doesn't know where that money could come from. The country's national security will not be imperiled, Blumenthal said, but rather the Navy will have to do more with less.

"We were counting on the Miami to be part of the force for the next eight or nine years," said U.S. Rep. Joe Courtney, D-2nd District. "The undersea fleet is really performing at an extremely high tempo, and losing one of our attack subs is just going to put added strain, not just for a year or two but over a long period of time."

The new Virginia-class attack submarines cost about $2.6 billion each. Both Blumenthal and Courtney said the potential loss of the Miami - either temporarily for repairs or permanently - underscores the importance of continuing to build two Virginia-class submarines a year to replace the aging Los Angeles class. And, they agreed, if the Navy decides to repair the Miami, Electric Boat is the shipyard for the job.

The Navy contracted with EB for about $120 million worth of repairs to the USS Hartford after the Los Angeles-class submarine collided with a Navy amphibious ship in the Strait of Hormuz in 2009. The biggest problem was that the sail had crushed into the pressure hull. The patch to fix the hull measured more than 150 square feet.

"The USS Hartford showed that what was pretty grim-looking damage was actually salvageable and EB was instrumental in terms of making that happen," Courtney said.

There's no question EB will be "part of the solution if the Navy decides that's the way they want to go forward," Courtney added.

EB has not been asked to send anyone to the naval shipyard, said Robert Hamilton, a company spokesman. But, he said, the company is "ready to do whatever the Navy wants us to do."